This invention relates to an improvement in the master cylinder for a hydraulic motor-vehicle brake system and more particularly, to an improved fluid-tight connection between the brake fluid reservoir and the cylinder of a master cylinder.
There is known a master cylinder for a hydraulic motor-vehicle brake system, essentially comprising a reservoir for brake fluid which is made of plastic material and a metallic cylinder connected to the brake fluid reservoir in a mutually communicative fashion. The reservoir has a circular opening in the bottom wall thereof and the cylinder includes a tubular extension having an internally threaded axial bore and vertically extending from the cylinder at right angles thereto to provide connection between the cylinder and the reservoir. The bottom opening of the reservoir and the tubular extension of the cylinder are vertically aligned with each other. The upper end of the tubular extension directly contacts the lower surface of the bottom wall of the reservoir along the lower peripheral edge of the opening therein. A bolt having an axial bore therethrough extends through the reservoir bottom opening and the cylinder tubular extension with a slight annular clearance left between the peripheral wall of the reservoir opening and the outer surface of the stem of the bolt. The lower face of the head of the bolt rests upon a washer, which in turn rests upon the upper peripheral edge of the reservoir bottom opening. The external thread provided on the stem of the bolt is engaged with the internal thread on the tubular extension of the cylinder to connect the reservoir and the cylinder. In the construction hereinabove described, however, the force applied to the bolt to tighten it is directly transmitted to the reservoir which is made of plastic material. Since plastic material can only withstand a relatively small compressive stress, it is usually impossible to tighten the bolt by applying a torque which is large enough to connect the reservoir with the cylinder in a satisfactorily fluid-tight manner. A further disadvantage of the device known in the art as hereinabove described is also due to its construction hereinabove described in which the bolt directly connects the reservoir and the cylinder. Because of the well-known tendency of plastic material to reduce its volume when heated, variation in the ambient temperature which frequently takes place on a motor-vehicle causes frequent dimensional changes in the plastic material of the reservoir. Since the bolt directly connects the reservoir to the cylinder, those frequent dimensional changes in the reservoir material in an area adjacent to the bolt very often loosens the bolt, and brake fluid flows out through the clearance formed between the bolt, the bottom wall of the reservoir and the upper end of the cylinder tubular extension upon loosening of the bolt.